1. Field of the Invention
The present invention relates to a magnetoresistive head using a spin-valve element and a magnetic recording-reproducing apparatus having the magnetoresistive head installed therein.
2. Description of the Related Art
In recent years, recording density is being improved in the magnetic recording-reproducing apparatus such as an HDD. As a result of improvement in the recording density, the size of a recording bit that is a recording unit in a recording medium is reduced, and a signal magnetic flux generated from the recording medium is also made lower. Under the circumstances, a high-sensitive magnetoresistive head (MR head), which directly senses the medium magnetic flux by utilizing a magnetoresistive effect, has been put to the practical use.
Nowadays, a spin-valve element (SV-GMR) comprising a spin-valve (SV) film including a magnetization pinned layer (pinned layer)/an intermediate layer (spacer layer)/a magnetization free layer (free layer) and generating a giant magnetoresistive effect is used as a sensor element of the MR head.
The conventional SV-GMR head is a shielded SV head comprising an SV element and a pair of magnetic shields having the SV element sandwiched with interposing a pair of magnetic gaps and the SV element is a so-called CIP (Current-In-Plane)-SV element in which a sense current is made to flow in the in-plane direction parallel to the surface of the SV film.
Recently, a so-called CPP (Current-Perpendicular-to-Plane)-SV element, in which the sense current is made to flow in the perpendicular direction to the surface of the SV film, is proposed. Since the CPP-SV element shows improved magnetoresistance ratio (MR ratio), it can be expected that a GMR head having a high output will be realized.
Where further improvement in the recording density of the recording medium is attempted, it is required to reduce the track width and the bit length. However, since it is necessary to form a CIP-SV element or a CPP-SV element between the magnetic shields in the shielded SV head, a reduction in the distance between the shields and a reduction in the gap length are limited so as to make it difficult to comply with the requirement for the reduction in the bit length.
For example, Japanese Patent Disclosure (Kokai) No. 6-325329 teaches a structure that a magnetic underlayer for sensing an external magnetic field is formed to extend from the air-bearing surface in the height direction of the head and the magnetic underlayer is coupled with a magnetization free layer formed on an inner part remote from the air-bearing surface. In this structure, a nonmagnetic intermediate layer and a magnetization pinned layer are formed on the magnetization free layer, and the magnetic underlayer alone is formed near the air-bearing surface.
As described above, the reduction in the gap length is limited in the shielded GMR head and, thus, it is difficult to comply with the requirement for the reduction in the bit length in the magnetic recording-reproducing apparatus.